Design of 0.92 Ghz artificial magnetic conductor for metal object detection in RFID tag application with little sensitivity to incidence of angle.

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

E-ISSN: 1817-3195

DESIGN OF 0.92 GHZ ARTIFICIAL MAGNETIC
CONDUCTOR FOR METAL OBJECT DETECTION IN RFID
TAG APPLICATION WITH LITTLE SENSITIVITY TO
INCIDENCE OF ANGLE
1

M. ABU, E. E. HUSSIN, A. R. OTHMAN, FAUZI. M. JOHAR, NORHIDAYAH M. YATIM,
2
ROSE. F. MUNAWAR
1

Universiti Teknikal Malaysia Melaka, Faculty of Electronic and Computer Engineering
2
Universiti Teknikal Malaysia Melaka, Faculty of Manufacturing
E-mail: maisarah@utem.edu.my, eryana88@hotmail.co.uk, rani@utem.edu.my, fauzi@utem.edu.my,
norhidayahm@utem.edu.my, rosefarahiyan@utem.edu.my
ABSTRACT
In this paper, the new structure of Artificial Magnetic Conductor is presented. The AMC is designed to
overcome the failure of detecting the RFID tag when placed near to the metal based object. It is too
complicated to design an AMC at low frequency due to limitation of size and bandwidth. In this paper, the
0.92 GHz AMC is designed with different sizes and shapes of slots inserted into the square PEC patch. The
size of single unit cell of this AMC is 45.5 mm x 45.5 mm. The AMC is designed in stacked layer to
increase the bandwidth of single unit cell. The optimized AMC at 0.92 GHz frequency, had increase the
performance of dipole antenna by return loss = -21.8 dB, gain = 3.0 4dB and directivity = 5.149.
Keywords: Artificial Magnetic Conductor, RFID, Metal object detection
1.

INTRODUCTION

Radio Frequency Identification, RFID is not new in
the world of technology today. In 1945, the idea of

activating a device from outside source has been
invented for military by retransmitting the radio
wave into audio information.
Today, the
emergence of RFID technology system has makes
work easier. The use of RFID can be seen in
various sectors such for baggage handling, tolling
system and also an anti-theft system. The basic of
RFID system consists of one reader, one antenna
and some piece of tags. The tag can be an active or
a passive type. For passive-type tag, the size is
smaller than the active-type because it has no
battery attached. The communication between the
reader and tag is called backscattering modulation.
The reader’s antenna will transmit the
electromagnetic wave into all directions. Any tag
within that transmitting area will be activated by
this electromagnetic wave. Then, wave will be
retransmitted back to the reader. RFID system
allows two-way communications between the

reader and tag. Therefore, the system needs at least
one device to monitor and operate the read and
write process. Some add a speaker (to produce
‘beep’ sound) or LED (to emit light) to indicate

successful read and write process for each tags. The
RFID system frequency operated from 120 kHz to
10 GHz. Higher frequency systems can support
longer reading range but the tag size will
exceedingly bigger. Table 1 shows the list of RFID
frequencies and the reading distance as provided in
the market.
Table 1: List Of RFID Frequency With Reading
Distance And Example Of Application
RFID
system

Frequency
range

Reading
distance

LF

120-150 kHz

10 cm

HF

13.56 MHz
443 MHz
(short-range)
865-868 MHz
(Europe)
902-928 MHz
(North
America)
2450 – 5800

MHz (ISM
band)
3.1 GHz – 10
GHz (Ultrawide band)

10 cm – 1m

Example of
application
Animal
Identification
Smart Card

1m – 100 m
1m – 12m

Military (with
active tag)

UHF

Microwave

1m – 2m
802.11
WLAN
Up to
200 m

Figure 1 shows the communication between
three RFID tags in three different conditions. Tag A

307

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

is placed within transmission area of reader’s
antenna. Therefore, the transmitting and receiving
process happens. Tag B is placed outside of the
transmitting area so it will stay in active. Even that
Tag C in the transmitting area, the persistence of a
metal plate at the back of tag had reflected all the
transmitted electromagnetic wave. Therefore, Tag
B and Tab C failed to operate. The problem for Tag
C is due to the existence parasitic capacitance
between tag and metal object. Therefore, the gain
and efficiency of the tag will decrease causing total
malfunction to the system. Besides, the reading
distance between tag and reader also will be
decrease. To overcome this problem, the tag needs
to be placed at distance of quarter- wavelength
apart from the metal object to reduce the
suppression of surface wave. Another method is by
placing the dielectric material layer at the back of

the RFID tag [1-3].

Figure 1: The Communication Of RFID Tags

Artificial Magnetic Conductor, AMC is one of
metamaterial structure that is designed to increase
the performance of an antenna [4-6]. The use of
AMC had been proved to increase the gain of the
antenna by reducing the undesired back radiation
and mutual coupling. In this paper, AMC will solve
the problem of RFID Tag positioned on metal
object. The AMC will be applied as the ground
plane to redirect the radiation reflected by the
metallic object. The AMC structure/design consists
of AMC patch, substrate and ground layer. The
AMC patch and ground layer are made by perfect
electric conductor, PEC. The PEC is a material that
exhibits an intrinsic electric conductivity that will
reflect the incidence wave to other directions. The
reflection phase of the PEC material characterized

at ±180˚ while for AMC (at resonant) characterized
at ±90˚ phase at free space.
Most of the RFID tag in the market is designed
as dipole-type antenna. By applying AMC at the
antenna ground plane may increase the gain and

E-ISSN: 1817-3195

reduce the backscattered / mutual coupling caused
by the metal object. Result of comparison between
four types of AMC in paper [7] stated that the
mushroom-like EBG surface gives better bandwidth
and gain performance than others AMC design
when placed on a low-profile antenna at 2.45 GHz.
This is due to the existence of via hole that
connects the patch to the ground plane. However,
this AMC structure is complex and the fabrication
process is more complicated. The AMC behaves as
in-phase reflection between the incidence and
reflected electric field. The artificial term in AMC

is used instead of the Perfect Magnetic Conductor
because PMC is not exists in nature. However,
AMC satisfy the physical character of PMC at
certain frequency band [8].
In this paper, the AMC will be designed at low
frequency 0.92 GHz by using Rogers R03010
substrate. It is difficult to design at low-frequency
because the structure will be intensely big. In [910], the square AMC patch and zigzag AMC were
designed using substrate thickness of 6.35 mm.
Some design has introduced space filling into the
design to reduce the dimension of the AMC but the
bandwidth is reduced. In [10], two types of
miniaturized AMC proposed with increased
bandwidth value. Yet, the structure is very
complex.
When applying the single cell AMC to the lowprofile antenna, each single cell will be arranged in
array order. The existence of AMC to the back of
the low-profile antenna will change the value of
gain, directivity and return loss of the single lowprofile antenna. Different size of AMC shows
different result at certain frequency. The AMC

designed in [8], the 250 mm x 350 mm AMC shows
better result than the 43 mm x 129 mm AMC. But
the reading distance for larger AMC is decreased.
Another characteristic that must AMCs have is the
stability to the incidence of angle. In [11] a novel
flexible AMC was designed by using bendable type
substrate. The prototype has been manufactured and
measured under flat and bent condition. The
simulation result shows ±8° as a limitation of
bending stability.
2.

SINGLE UNIT CELL OF SQUARE AMC
AT 0.92 GHZ

The first step is to design a single cell AMC
structure. This part will discuss the basic square
shape structure of AMC designed at 0.92 GHz by
using Rogers RO3010 as a substrate with εr = 10.2

308

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

and thickness = 1.28 mm. From the simulation
result of single cell AMC in Figure 2(a), the
reflection phase falls on 0.9147 GHz and 0.9366
GHz at 90° and -90° respectively. Figure 2(b)
shows the real and imaginary impedance of AMC.
AMC is expected to have very high real impedance
at resonance.

Reflection Phase (°)

150
100
50
0
-50
-100
-150
0.86

0.88

0.90

0.92

0.94

0.96

0.98

1.00

Frequency (GHz)

(a)
1200

Impedance (Ohm)

1000

Real
Imaginary

800
600
400
200
0

E-ISSN: 1817-3195

decreased by 0.91% and 6.50% respectively. So in
order to ovoid bandwidth reduction, the smallest
slot will be selected. Then for the second step, the
structure is introduced to multiple size of slot at
each size of the square AMC as in Figure 3(b).
Each size will have four 1 mm x 2 mm slots, two 2
mm x 4 mm slots and one 2 mm x 8 mm slot. The
result is shown in Figure 4(b). The frequency is
reduced from 0.93 to 0.88 (3.78%). Step three, one
horizontal rectangular slot with dimension of 2 mm
x 7 mm is inserted to each side of the AMC as in
Figure 3(c). The decrement of frequency is about
0.96%. Next, four ‘plus’ shaped slot is inserted as
in Figure 3(d). Now, it causes additional reduction
of frequency to 1.64%. For the last step, one slot
will be inserted to the center of AMC. Two types of
slots will be discussed. First, for the square slot in
Figure 3(e), the frequency decrement is very small
(0.22%). Plus it causes more bandwidth reduction
to 12.05%. For ‘plus’ shaped slot in Figure 3(f), it
give more frequency decrement to 2.54%. Figure
4(c) shows the graph of square and plus shaped slot
applied to the center of AMC. Through the shape
modification in Figure 3, the bandwidth had
reduced from 2.25% to 1.86%. In order to increase
the bandwidth, some modification will be made to
the thickness of the AMC.

-200
-400
-600
-800

0.88

0.90

0.92

0.94

0.96

0.98

Frequency (GHz)

(b)
Figure 2: (A) Design Structure (B) Reflection Phase And
(C) Surface Impedance Of Square AMC

(a)

(b)

(c)

3. STACKED WAFER AMC AT 0.92 GHz
In this part, new AMC structure is designed to
reduce the dimension of the basic square AMC. By
applying slots into the first layer of PEC patch can
helps to reduce the resonant frequency of AMC.
Thus, the new structure will be designed with
multiple slots with different size and shapes. Figure
3 shows the process of adding slots into the new
design. The final structure is illustrates as in Figure
3(e). Firstly, slots with 1 mm x 2 mm is inserted
and arranged in Figure 3(a). For the structure in
Figure 3(a), three different sizes of slots are
presented. The spacing between each slot is same
for each square side. The reflection phase graph in
Figure 4 shows that by applying different size of
slot will change the value of resonant frequency
and bandwidth.
From Figure 4(a), when the size of slot is
increase, both frequency and bandwidth is

(d)
(e)
(f)
Figure 3: The Variation Of Slots Introduced Into The
New Design.

The value of bandwidth can be increased by
adding the thickness of the substrate. In this paper
two types of thickness modification will be
discussed. The detailed image of the thickness
modification is shown in Figure 5. The modified
AMC structure in Figure 3(f) is optimized at 0.92
GHz frequency. The thickness reduced from 52 mm
x 52 mm to 45.5 mm x 45.5 mm. The structure in
Figure 5(a) is a single layer AMC with overall
thickness of 1.98mm. The bandwidth percentage is
1.86%. Then the thickness of substrate is doubled

309

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

as in Figure 5(b). Now the bandwidth increases to
2.04%. For the structure in Figure 5(c), 2 layer of
AMC is stacked on the ground plane. The thickness
is increase to 2.665 mm. Calculated bandwidth for
stacked layer AMC is increased to 3.86%. Figure 6
shows the simulation result for thickness
modification illustrated in Figure 5.

E-ISSN: 1817-3195

Figure 5: Thickness Modification (A) Single Layer, (B)
Substrate With Double Thickness (C) Stacked Layer

200
150

150

Reflection Phase (°)

Reflection Phase (°)

200
100
50
0
-50

1 mm x 2 mm
1 mm x 4 mm
2 mm x 4 mm

-100
-150
-200
0.86

0.88

0.90

0.92

0.94

0.96

100
50
0
-50
-100

0.98

Frequency (GHz)
(a)

-150
-200
0.86

200

0.88

0.90

0.92

0.94

0.96

0.98

1.00

Frequency (GHz)
Reflection Phase (°)

150

Stacked AMC
Double thickness substrate
Single layer AMC

100
50

Figure 6: Thickness modification of AMC

0

3.

-50
-100

Figure 3(a)
Figure 3(b)

-150
-200
0.80

0.82

0.84

0.86

0.88

0.90

0.92

0.94

0.96

0.98

Frequency (GHz)
(b)
200

Reflection Phase (°)

150
100
50
0
-50

-100

Square shaped slot
Plus shaped slot

-150
-200
0.76

0.78

0.80

0.82

0.84

0.86

Frequency (GHz)

0.88

0.90

0.92

(c)
Figure 4: Reflection Phase Of Wafer AMC With (A)
Different Of Slots Size (B) Addition Slot As In Figure
3(A) And (B), (C) Square And Plus Shaped Slot

ANGLE OF INCIDENT

The study in angle of incidence of plane wave
on AMC is important to find out the AMC stability.
In [13], the Jerusalem cross patch metallization
shows more stable than the square patch and square
ring AMC. In this part, the stability of square
AMC and stacked wafer AMC will be investigated.
Figure 7 shows the reflection magnitude and phase
of AMC at different incidence angles. From the
reflection phase in Figure 7(b) and (d) shows that
the graphs are very close to zero at 0.92 GHz
frequency. The bandwidth for both AMCs is
increase from 0° to 60°. The bandwidth is increased
to 1.27% and 1.82% for square and Stacked Wafer
AMC respectively. The frequency of square AMC
varies from 0.92 GHz at 0° until 0.93 GHz at 60°.
While for Stacked wafer AMC the frequency varies
from 0.92 GHz at 0° to 0.9256 GHz. Herein, both
square and stacked wafer AMCs show good
stability when dealing with different angle of
incidence.

310

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

E-ISSN: 1817-3195

4. DIPOLE ANTENNA AND
WAFER AMC AT 0.92 GHz

STACKED

Magniture (dB)

-0.5

In this part, the dipole antenna will be used to
represent the RFID tag. The purpose of this paper is
to overcome the problem of metallic object
detection in RFID, so it required non-complex
dipole antenna design. Table 3 shows the detailed
result for optimized stacked AMC at 0.92 GHz. The
use of wafer stacked AMC to the back of the dipole
antenna had increased the return loss value (in
negative side) and gain of the antenna. The table
shows that when the metal plate is applied, the gain
of the antenna dropped to -13.60 dB and the
efficiency of the antenna become poor. The single
cell of stacked wafer AMC designed in part 3 has
been optimized at 0.92 GHz. The structure of
stacked wafer AMC is shown in Figure 8.

0°
10°
20°
30°
40°
50°
60°

-1.0

-1.5

-2.0
0.90

0.91

0.92

0.93

0.94

Frequency (GHz)

(a)
150

Reflection Phase (°)

100
50

0°
10°
20°
30°
40°
50°
60°

0
-50

-100
-150
0.88

0.90

0.92

0.94

0.96

0.98

Frequency (GHz)

(b)
-0.2

Magnitude (dB)

-0.4
-0.6

0°
10°
20°
30°
40°
50°
60°

-0.8
-1.0
-1.2
-1.4
0.88

0.90

0.92

0.94

Figure 8: 3 X 1 Stacked Wafer AMC Optimized At 0.92
Ghz
Table 2: Simulation Result For Dipole Antenna, Dipole
Antenna With Metal Object And Dipole Antenna With
Stacked Wafer AMC

0.96

Frequency (GHz)

(c)

Dipole
antenna

Dipole
antenna
and metal

Dipole
antenna and
stacked wafer
AMC

-14.74

-0.22

-21.81

1.98

-13.60

3.04

2.07

5.38

5.15

97.93

1.26

82.35

150

Reflection Phase (°)

100
50

-50
-100
-150
0.88

Return Loss,
dB
Gain, dB
Directivity,
dBi
Efficiency,
%

0°
10°
20°
30°
40°
50°
60°

0

0.90

0.92

0.94

0.96

Frequency (GHz)

(d)
Figure 7: (A) Magnitude And (B) Reflection Phase Of
Square AMC (C) Magnitude And (B) Reflection Phase Of
Stacked Wafer AMC.

From Table 3, the use of stacked wafer AMC
to the dipole antenna had increase the gain and
return loss of the antenna. When the metal plate is
applied to the back of the antenna, the value of gain
become negative and the efficiency of the antenna
drops to 1.26%. This means that the antenna is
failed to operate when placed directly/near to metal
based object. By applying AMC to the back of the
311

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

antenna, it not just overcomes the problem cause by
the metal object, but it also increase the
performance of the antenna itself.
The prototype of the wafer stacked AMC is
shown in Figure 9. The fabrication process is very
simple and not requires higher cost. Using the
RFID reader from the market, the reading distance
of the AMC is measured. First, the distance for
RFID is measured and the highest distance for
RFID tag is measured at 5 meters. Then, the metal
plate is placed at the back of the RFID tag. The
RFID reader produces no sound even that the tag is
placed very near to the reader’s antenna. When, the
stacked AMC is placed between the RFID tag and
metal plate, the longest reading distance is
measured at 2.5 meters.

(a)

(b)
Figure 9: The Prototype Of Wafer Stacked AMC Applied
To RFID Tag On (A) Flat And (B) Curve Surface

5.

CONCLUSION

For the conclusion, the use of AMC is proved to
provide shielding to the antenna from the metal
object. In this paper, the new structure of wafer
stacked AMC has been proposed for RFID
application at 0.92 GHz frequency. The substrate
used in this paper is a bendable type so it can be
applied to limited bending curve surface.

E-ISSN: 1817-3195

ACKNOWLEDGEMENT
The authors wish to thank the Centre for Research
and Innovation Management (CRIM) of Universiti
Teknikal Malaysia Melaka (UTeM) for the support
of this work under the grant number of PJP/2012/
FKEKK (27B) S01030.
REFRENCES:
[1]. D. Yan, Q. Gao and N. Yuan, “Strip-Type
AMC Structure and Analysis to Its Band-Gap
Characteristics” Progress in Elecromagnetics
Symposium 2005,pp. 505-509, Aug. 2005.
[2]. E. Carrubba, A, Monorchio, and G. Manara
“Artificial Magnetic Surface for Circular
Polarization Movemenent” Microwave and
Optical Technology Letters, Vol 5, pp.17821786, Aug 2010.
[3]. M Elena de Cos, Yuri Alvarez and Fernando
Las-HEras, “Design and Characteristics of
Planar Artificial Magnetic Conductor in the
RFID SHF Band” Proceeding of Forth
European Conference on Antenna and
Propagation 2010, pp. 1-5, Apr 2010.
[4]. Ramona Cosmina Hadarig, M. Elena de Cos,
and F. Las-Heras, “UHF Dipole-AMC
Combinationfor RFID Applications”, IEEE
Antennas And Wireless Propagation Letters,
VOL. 12, pp: 1041-1044, 20013.
[5]. Haider R. Raad, Member, IEEE, Ayman I.
Abbosh, Student Member, IEEE, Hussain M.
Al-Rizzo, and Daniel G. Rucker, “Flexible and
Compact
AMC
Based
Antenna
for
Telemedicine
Applications”,
IEEE
Transactions On Antennas And Propagation,
Vol. 61, pp: 524-531, 2013.
[6]. B. S. Cook, Student Member, IEEE, and A.
Shamim, Member, IEEE, “Utilizing Wideband
AMC Structures for High-Gain Inkjet-Printed
Antennas on Lossy Paper Substrate”, IEEE
Antennas And Wireless Propagation Letters,
Vol. 12, pp: 76-79, 2013.
[7]. J. R. Sohn, K. Y. Kim, H. –S. Tae,
“Comparative Study on Various Artificial
Magnetic
Conductors
for
Low-Profile
Antenna” Progress in Electromagnetics
Research, PIER 61, pp: 27-37, 2006.

312

Journal of Theoretical and Applied Information Technology
20th February 2014. Vol. 60 No.2
© 2005 - 2014 JATIT & LLS. All rights reserved.

ISSN: 1992-8645

www.jatit.org

[8]. Y. Liu, K.M.Luk, H.C.Yin, “A RFID Tag
Metal Antenna on A Compact HIS Substrate”
Progress in Electromagnetic Research Letter,
Vol 18, 2010, pp:pp:51-59.
[9]. S. Barbagallo, A. Monarchio and G. Manara
“Small Periodicity FSS Screens with Enhanced
Bandwidth Performance” Electronic Letters,
Vol 42 No 7, 2006.
[10].
M. Abu, K.A. Rahim, “Single-band and
Dual-band Artificial Magnetic Conductor
Ground Planes for Multi-band dipole
Antenna”, Radioengineering, Vol 21 No. 4,
2012, pp: 999-1006.
[11].
M. Abu, M. K. A. Rahim, “Single-band
Zigzag Dipole Artificial Magnetic Conductor”,
Jurnal Teknologi UTM, Penerbit Universiti
Teknologi Malaysia, pp. 19-25, 2012.
[12].
M. Hosseini, A. Pirhadi, and M. Hakkak,
“A Novel AMC With Little Sensitivity To The
Angle Of Incidence Using 2-Layer Jerusalem
Cross FSS”, Progress In Electromagnetics
Research, PIER 64, pp: 43-51, 2006.
[13].
Alireza Foroozesh, and Lotfollah Shafai,
“Investigation Into the Application of Artificial
Magnetic
Conductors
to
Bandwidth
Broadening, Gain Enhancement and Beam
Shaping of Low Profile and Conventional
Monopole Antennas,” IEEE Transactions On
Antennas And Propagation, Vol. 59, No. 1,
January 2011, pp: 4-20, 2011.

313

E-ISSN: 1817-3195